Systems and methods for aiding a driver to regain control of a motor vehicle when it becomes unstable has been a focus of research for some time. The most common types of unstable conditions are generally referred to as “understeer” or “oversteer” slides. An understeer slide is the situation where the front end of the vehicle moves toward the outside of a turn instead of following the curvature of the turn. An oversteer slide is the situation where the rear of the motor vehicle moves toward the outside of the turn (i.e., fish-tailing).
One system known to correct or minimize an understeer or oversteer slide is a torque vectoring differential (TVD). Typically, a TVD is an electronically-controlled differential that can create an understeering or oversteering moment about the center of gravity of a motor vehicle independent of the speeds of the wheels. In other words, a TVD is able to distribute engine power to a wheel regardless of whether that particular wheel is rotating at a faster or slower rate than the other wheel sharing the differential. In this manner, a TVD is different from a Limited Slip Differential (LSD), which generates understeer or oversteer moments as a function of distributing the wheel speed from the faster rotating wheel to the slower rotating wheel across the differential. Accordingly, a TVD utilizes the concepts of understeer and oversteer gradients to affect the dynamics of the vehicle. Thus, the ability of a TVD to create an understeering or oversteering moment about the center of gravity of the vehicle independent of the speeds of the wheels, up to a fixed limit of wheel speed difference (i.e., a saturation point), greatly increases the range of authority that a TVD has on vehicle dynamics, as compared with an LSD.
A TVD typically includes one or more sensors in communication with one or more controllers (e.g., microcontrollers). The sensors are located at a variety of places on the vehicle and continually monitor the vehicle for any signs of instability. Once instability is detected, the sensors notify the controller(s), and once notified, the controller(s) provide differing amounts of power to the wheels such that the wheels are able to rotate at different rates. By rotating the wheels at different rates, a TVD is able to correct or minimize the effects of an understeer or oversteer situation by creating an understeer or oversteer moment at the center of gravity.
Another system to help the driver regain control of the vehicle when the vehicle begins to experience instability is a stability control system (SCS). Typically, an SCS include one or more controllers (e.g., microcontrollers) coupled to one or more sensors located at various places on the vehicle that are able to detect understeer and oversteer slides. Once an understeer and oversteer slide is detected, the sensors notify the controller(s), which “automatically” applies braking to one or more wheels to thereby stabilize the vehicle. In other words, an SCS is designed to deliver transparent intervention the moment a situation becomes unstable by applying the brakes at one or more selected wheels depending on whether the unstable condition is a left-turn or right-turn understeer slide, or a left-turn or right-turn oversteer slide.
An SCS is more effective for correcting or minimizing an understeer or oversteer slide than a TVD; however, because an SCS utilizes the vehicle's brakes to correct or minimize an understeer/oversteer slide, a significant amount of the vehicle's energy is converted into mechanical “heat” (i.e., kinetic energy is lost). By contrast, although utilizing a TVD to correct or minimize the effects of an understeer/oversteer slide is less effective than an SCS, a TVD is more efficient from an energy loss point of view. Moreover, although a TVD is not as effective as an SCS, a TVD is sufficient to correct or minimize the effects of most understeer and oversteer slides. Accordingly, it is desirable to provide a system and method for integrating a TVD with an SCS to provide a more efficient system of regaining control of a vehicle experiencing an unstable condition. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.